This invention is related to battery modules for electric vehicles. More specifically, the subject of this invention is a battery module containing Lithium-polymer pouch type unit cells and having a thermal management system.
With the trend toward higher pack voltages and the use of Lithium-based batteries, the scope and complexity of fraction battery packs has increased. Depending on the required voltage, a typical battery pack is often comprised of a large number of individual unit cells, these cells being arranged in various series-parallel combinations. It is often desirable to group these cells into modules, which simplifies and standardizes the battery pack assembly process. The modules are typically of a size and weight that they can be lifted by a single person.
For many electric automobiles, the optimum placement of the battery pack is beneath the passengers and approximately mid-vehicle between the front and rear axles. When so located, the battery pack can be attached to the frame of the vehicle in such a manner that it is removable from the bottom of the vehicle. Additional benefits of this location include a favorable front-rear weight distribution and a low center of gravity. A practical height of such a battery pack from the top to the bottom of the enclosure is approximately 15 centimeters, and this height restriction imposes certain design constraints on the modules.
Pouch type cells are relatively flexible and vulnerable to impact and abrasion, and assembling large numbers of these cells into a rigid module can be difficult. The battery module assembly must provide means of supporting the cells and ensuring that they are not degraded by road forces. Further, it is desirable to maintain a consistent geometry as the cells tend to expand and contract during charge and discharge cycles.
Thermal management of pouch cells can also be difficult. When pouch cells are stacked together, the sides of the assembly are usually flexible and uneven, making it difficult to interface the assembly with a thermal management system. The prior art has included such solutions as the use of heavy and expensive metal fins interposed between the cells to extract heat.
Modules having a large number of unit cells require reliable high current connections between the cells. Degradation of a single connection can lead to battery pack failure with potentially dangerous results such as fire. Therefore, ensuring the integrity of the power circuit is critical to the proper functioning of the pack. The selected interconnect method should provide reliable, low resistance connections with minimum parts count.
Prior art battery modules may not satisfy the requirements for traction battery modules. Therefore, an improved battery enclosure is needed.